Some published adventures seem to suggest so
The PHB says
Copying that spell into your Spellbook involves reproducing the basic form of the spell, then deciphering the unique system of notation used by the Wizard who wrote it. You must practice the spell until you understand the Sounds or gestures required, then transcribe it into your Spellbook using your own notation.
Note that this is a four-step process:
- reproduce the basic form of the spell
- decipher the unique system of notation
- practice the spell until you understand it
- transcribe it using your own notation
Even though this whole process is what is required to 'copy a spell into your spellbook', only the last step explicitly involves actually writing something in your Spellbook, and the first step does not say where you are reproducing it. Further, the cost given for time and materials is stated as the total cost for the process as a whole, and not broken down for each step (and see this question and this question).
Thus, I think it is possible that the first step, reproducing the spell's form, could involve just what you suggest, making a quick reproduction of the lines and shapes of the spell on some surface, perhaps not even your spellbook, without understanding what any of them mean. Steps (2) and (3) are likely where most of the time and money are spent, trying to figure out what the symbols mean and how to actually cast the spell. As you note, making a 'back-up' copy of a spell you already know has a specifically delineated time and cost less than that of deciphering an unknown spell, so the replacement cost might be assumed to be entirely equivalent to step (4).
Have a read of the community wiki answer to Thomas Markov's question Do any published adventures contain spells a wizard can copy that aren't written in a spellbook?, in particular for the five rocks in Storm King's Thunder and the statue in the Dungeon of the Mad Mage.
From Storm King's Thunder,
Chapter 10 says, in Room 25 - Library (p. 212):
Five rocks have the following wizard spells inscribed on them: antimagic field, conjure elemental, fabricate, legend lore, and stone shape. The rocks function like pages of a spellbook, but each weighs 600 pounds. A character who has a spellbook can record these spells in it.
The rocks weigh enough that the characters are unlikely to be taking them with them, and certainly wouldn't have the permission of their owners to do so. While combat can occur at the greater location in which these rocks are placed, it is not in an area that is actively hostile to the characters. Still, the characters are unlikely to be there for long. If they are unsuccessful in their goals while at the location, they will be defeated and expelled, imprisoned, or killed. If they are successful, they will quickly move on. Neither scenario argues for them spending much time at the location.
One of the spells available is 8th level. The rules for 'deciphering and copying' a spell would require that any wizard not of the abjuration school needs access to the rock for 16 hours. To collect several of the spells would require days. If these rocks are indeed placed for wizard characters to gain these spells, then ask yourself what seems more likely: that the wizard can record the symbols as undeciphered patterns in their book and then decipher and copy them later after having left the location, or that the characters are meant to stay at this location for hours or days and also happen to have thousands of gp of ink and experimental materials on hand?
In Dungeon of The Mad Mage there is a stone statue with a likeness of a spellbook from which a spell can be obtained:
On level 7, in the courtyard of Maddgoth's Castle (p. 102)
Statue. In the center of this open-air courtyard, surrounded by gardens of glittering, pebble-sized crystals, stands a 9-foot-tall statue of a plump human wizard (...) reading from a spellbook. (...)
Carved into the pages of its open spellbook is the Mordenkainen's Sword spell. A wizard can take a rubbing of the spell and copy it into a spellbook.
Here the text explicitly says "A wizard can take a rubbing of the spell and copy it into a spellbook." So what does this mean? 'A wizard can take a rubbing of the spell [now] and [later follow the rules to decipher and] copy it into a spellbook', or 'A wizard can take a rubbing of the spell [now] and [then immediately spend 14 hours and 350gp of materials to] copy it into a spellbook [but only at this location]'?
Both of these passages, in my opinion, suggest that it is possible to collect a version of a spell in no more time than it would take to recreate the actual symbols without understanding them, and then later do the time-consuming process of changing them into one's own notation.
A note on terminology
The process of placing a spell into one's spellbook is called by the PHB 'deciphering and copying'. I think it may be deliberate that in neither of these two cases do the adventures refer to wizards 'copying' the spells that are available - rather, in the first they 'record' the spell, and in the second, they 'take a rubbing'. For me, this is a clue that wizards are indeed permitted to separate out step (1) of the overall spell copying process from the other steps.
If you agree, you might change the title of your question from 'Can a wizard copy' to 'Can a wizard record'.